Equipment employing spaced apart moving endless conveyor belts as the mold surfaces for continuous foam panel products is old and generally well known to those in the art. Numerous devices have been proposed, see e.g., U.S. Pat. Nos. 3,082,861 and 3,093,232. Continuous foam molding apparatus have been commercially available for many years. Many of these devices incorporate one or more improvements which have been made over the years such as the use of pneumatic clamping means, U.S. Pat. No. 3,568,245; the use of micro-switches to sense pressure build-ups between the belts, U.S. Pat. No. 3,994,648; side clamps, U.S. Pat. No. Re 29,125; panel type conveyors, U.S. Pat. No. 3,674,130; conveyor rails and rollers, U.S. Pat. No. 3,037,603; and the like.
In general, the production of continuous foam panels involves the use of a pair of continuous outer sheets of flexible material, such as paper, bent to include dependent sides. Respective sheets of material are fed to a molding machine having a pair of spaced apart endless belts so that each sheet is adapted to abut one of the belts. Foamable resins are continuously injected or spread between the sheets during operation of the machine. As the resin product travels between the belts, it begins to foam and expand to fill the space there and exert a pressure on the belts. These belts act as the mold cavity to constrain the foam and shape the final product.
While numerous improvements have been made in endless belt molding apparatus to provide more uniform products and attain high speed production, none of the prior art molding apparatus is capable of high speed molding at pressures in excess of 15 psi. Conventional endless belt molding apparatus operation with foam pressures ranging between 3 and 5 psi. One of the major problems associated with high pressure, high speed molding is that excess localized pressures can build-up during the foaming process. Unless that pressure is relieved, serious damage can result to the equipment.
Recent improvements in such equipment provide means for sensing such build-ups and to actuate controls to increase the spacing between the endless belts. A conventional method for protecting against excess pressure build-up, for example, U.S. Pat. No. 3,994,648, uses micro-switches to sense the pressure build-up by the disengagement of the switch contacts when such pressure raises one of the belts from the gauge block. The switches actuate an adjustable spacing means to lift the upper belt away from the product and completely relieve the pressure on the apparatus.
However, one of the disadvantages of such methods is that it normally results in a shutdown of the machine causing the product to backup. This results from the fact that the sensing means do not provide continuous monitoring of the pressure build-up, but rather an abrupt disengagement when a selected pressure is reached. Furthermore, conventional drive means do not permit synchronous rotation of the belts once a belt is raised. Accordingly, it is one of the objects of the present invention to provide an endless belt molding apparatus having means for continuously sensing pressure build-up during the molding operation and to permit relief thereof without stopping production. It is a further object of the present invention to provide a molding apparatus capable of operating with high pressure generating foam materials. It is still further object of the present invention to provide a drive means for synchronous rotation of the belts during vertical movement of the belts.